Theory of calculating randomness for damping factor
I figured it out.
public Vector3f damping(Vector3f vector) 
{
    float random = (float) (this.randomDamp*(Math.random()*2-1));
    float clampedValue = Math.max(0, Math.min(1, (1-damp)+random)); //clamp between 0 and 1
    vector.scale(clampedValue);
    return vector;
}

With a factor of 0.5 and a random factor of 1, the final factor will vary between -0.5 (0) and 1.5 (1)